Monoclonal Antibodies (MoAb) to the guinea pig line 10 hepatoma have been produced. Two clones were selected and put into ascites in mice. The original ascites fluid produced in BALB/c mice from clone C-2 titered to 1/1x10 to the six vs. line 10 hepatoma cells with minimal cross-reactivity to guinea pig line 1 and normal liver and spleen cells by live cell radioimmunoassays (RIA) utilizing iodinated protein A. By immunofluorescence (IF) and cytotoxicity (CTX) assays the cross-reactivity was as high as 30%. Isotyping showed the MoAb to be an IgG1. Frozen C-2 hybridoma cells have been put back into tissue culture and are no longer producing immunoglobulins. No further work with the C-2 clone is anticipated. Clone D-3 has been put in tissue culture and supernatant fluids show very high titer (1/5x10 to the four) vs. line 10 and no cross-reactivity with line 1 by RIA. Preliminary isotyping indicates a probable IgG1. The clone has been put into mice for ascites production, and complete characterization by RIA, IF and CTX will be done to determine specificity. Fluorescent activated cell sorting (FACS) analysis of specificity is underway. In vivo therapy experiments with the monoclonal antibody in this guinea pig needed will follow.